In an automated workpiece-machining apparatus it is important that the controller for the machine be able to verify whether or not the workpiece is in the proper position for machining. If the workpiece is not in place at all or out of position somewhat, substantial damage could occur when a machining operation is attempted.
Typically the workpiece is moved horizontally into position against a vertical support, to which it is secured by some form of clamp. In this arrangement the workpiece is forcibly pressed horizontally against the position detector.
When, however, the workpiece is on a horizontal support surface, the situation is somewhat more difficult to monitor, as normally only the workpiece weight is effective downward, the clamping force frequently remaining horizontal. To do this a thin metal foil is used as a position detector to check any gap between the workpiece and the support. Such a position detector is hard to use.